The present invention relates to rollers, drums and analogous rotary devices, and more particularly to improvements in rotary devices which exhibit the tendency to oscillate or vibrate during rotation, especially while supporting other rotary devices such as rolls or analogous supplies of convoluted paper webs or the like. Still more particularly, the invention relates to improvements in rollers which can be used in pairs or in groups of three or more to support and/or otherwise engage rotary parts, especially bobbins or reels of convoluted paper, synthetic plastic web stock or the like.
It is well known that a modern paper processing machine must turn out or otherwise process large quantities of paper web material or the like. This means that the parts which transport, convolute, unwind and/or otherwise treat webs or strips of paper, metallic foil, imitation cork, flexible cardboard, synthetic plastic material or the like must be driven at an ever increasing speed. Operation at elevated speeds invariably entails numerous problems including those which are attributable to vibrations of rotary parts, for example, vibrations or oscillations which are caused by improper balancing of rotary devices and are either negligible or acceptable at low speeds but cause serious problems (such as noise, pronounced wear and/or others) at elevated speeds. It will be readily appreciated that, as the stressing of rotary parts increases in response to increasing speed, the vibrations or oscillations of such parts become more pronounced and/or more frequent with the result that certain corrective measures must be undertaken in order to ensure satisfactory operation as soon as the RPM of such parts reaches a predetermined threshold value. Typical examples of apparatus or machines wherein oscillations of rotary parts are likely to create problems at relatively high speeds are those which serve for collection (rolling up) or unwinding of convoluted webs consisting of paper, synthetic plastic foil, metallic foil or the like. For the sake of simplicity and convenience, the invention and the problems which are solved by its advent will be described with reference to apparatus which serve to convolute webs of paper on cores or analogous holders to form reels, bobbins or similar supplies. However, it will be appreciated that the same problems arise and can be solved if the invention is embodied in apparatus for unwinding paper webs or like flexible strip materials from the cores of bobbins or reels.
In many presently known winding apparatus for paper webs, the outermost convolution of the supply of convoluted flexible strip material rests on two supporting rollers, at least one of which is driven by suitable motor means to rotate the core and the entire reel in a direction to collect the paper web. The reel is set into and maintained in rotary motion as a result of frictional contact between its outermost convolution and the external surface(s) of the driven supporting roller(s). If the supporting roller or rollers oscillate, the extent of frictional contact between their external surfaces and the outermost convolution of the reel which rests on the supporting rollers is merely reduced or can (at times) decrease to zero. It has been found that transverse oscillations of the supporting rollers are especially likely to affect the extent of frictional engagement between the peripheral surfaces of such rollers and the outermost convolution of the reel, irrespective of whether the reel is rotated in a direction to collect or to pay out the web. Transverse oscillations are undesirable because they temporarily reduce the magnitude of the force with which the outermost convolution of the reel bears against the peripheral surfaces of the supporting rollers. The result is that the torque which the supporting roller or rollers transmits or transmit to the reel fluctuates within a wide range. This, in turn, can influence the uniformity of the convolutions on the reel as well as the operation of the machine or machines which supply the web to and/or receive the web from the winding or unwinding apparatus. It was further determined that oscillations which are due to flexing of the supporting rollers (in contrast to oscillatory movements of the entire supporting rollers) are just as undesirable. In other words, the quality of a winding or unwinding operation can be affected by oscillations which involve movements of the entire supporting rollers with respect to their bearings as well as oscillations which involve recurrent movements of certain portions of peripheral surfaces of such rollers relative to the remaining portions of the peripheral surfaces. For example, a relatively long supporting roller is likely to flex in the middle, whereas the extent of flexure at the ends of such roller is negligible or nil.
It was already proposed to damp the vibratory or oscillatory movements of supporting rollers for reels of paper or the like by employing hollow rollers whose interior is filled, at least in part, with a flowable medium, e.g., water, particles of sand or the like. Such supporting rollers operate satisfactorily up to a certain speed. However, once the RPM of the supporting rollers which are filled, at least in part, with a flowable material reaches a given threshold value, their oscillations become even more pronounced than in the absence of flowable material because the confined material contributes to the unbalancing of the supporting rollers and causes even more pronounced vibratory movements.